When ships collide on the sea, mostly, it is considered that the collision occurs due to carelessness of a ship operator. However, the operator who operates the ship cannot focus on sailing at every moment and it is difficult to check and predict all circumstances which may occur while sailing.
That is, rather than by the ships that determine whether there is collision and measure against the collision in order to prevent the collision between sailing ships, it is more efficient that a ground control center checks the movement of all ships and predicts a dangerous situation and then if the possibility of a collision is high, notifies the corresponding ship.
Therefore, in all main domestic and foreign ports, a vessel traffic control system is provided and operated and a control system which prevents the collisions of the ships while the ship is sailing is provided.
In the related art, a controller intensively watches a control screen on which a position of the ship is displayed and checks a distance between the ships based on his experience to predict the possibility of a collision between ships. If the controller determines that the collision possibility is high, the controller controls a sailing route of the corresponding ships to control the traffic.
In the ship, the controller uses a radar device mounted in the ship to identify nearby ships and sails the ship while referring to the identified ship.
In the meantime, in accordance with the development of marine radio communication technology, an automatic identification system (AIS) is used in the ship to send ship information including its own identification information (for example, a name of the ship) to the control center so that the control center can clearly identify a ship located in any specific position on the sea. Generally, on the control screen of the control center, a current position of a ship or an aircraft is shown on a map together with the brief name of the ship or the aircraft thereby.
That is, the AIS provided in the ship transmits MMSI (maritime mobile service identity) information, position information (for example, latitude and longitude coordinates), and dynamic information through which the ship can be automatically identified to the control center to identify the ship and easily figure out the location to increase the control efficiency.
Examples of various information included in the AIS information will be represented in the following Table 1.
TABLE 1ClassificationContent of informationRemarksStaticship name, IMO number, callIf there is anyinformationsignchange,(ship data)type of shipfrequently inputlength, width, and breadth ofchanged mattershipposition of antenna(stern/bow/left and right ofcenter line)Dynamicposition of ship, course overAutomaticallyinformationthe ground, ground speed, andinput inheading direction of shipaccordance withsailing status (sailing orsailing status ofanchored)the shiprate of turn (optional)(manual input istilted angle (optional)also allowed))Sailingdraft of shipPeriodically andinformationdangerous cargomanually inputdestination and scheduledbefore and duringarrival timethe sailingroute plan (optional)TextImportant sailing or weathercommunicationinformation is included
A vessel traffic control system figures out the location and speed of the ship from the AIS information transmitted from the ship and receives the result sensed by the radar which is a heterogeneous sensor at a predetermined period in order to understand the position in real time and uses them.
Basically, a target is tracked using the radar such that a plurality of unspecified object information received by a radar transceiver is analyzed to find out a movement characteristic of the corresponding target and continuously estimate the subsequent movement situation of the target therefrom. The tracking through the radar includes a tracking error and a mathematical filter which may minimize the error is used. The tracking is performed in real time through a dynamic filtering technique in which the tracking filter repeatedly estimates and updates the track. A Kalman filter is a representative filter thereof.
For continuous detection in the target tracking process, it is required to select an exact target among several objects. That is, the target is tracked in a situation where a clutter or a noise is present so that a data association method which can exactly select a real target object among sensor measured values from an uncertain source other than the object target which is currently being tracked is required for exact tracking. After associating the data, a track which is continuously connected to each of the target is generated and several tracks may be present depending on the number of targets. Typically, such track information is received from multiple radars rather than a single radar, the tracks generated by the multiple radars are fused and repeated tracks are removed. In this case, in order to increase the precision for the position, a fusion filter is used.
The information fused from the several radars is asynchronously fused with the latitude and longitudinal coordinates received from the AIS rather than the radar, again. The vessel traffic control system fuses the radar information and the AIS information to determine a final position of the target and display the determined final position on the screen so that the controller identifies the position or the speed of the ship and give a control instruction.
In the meantime, the AIS of the ship estimates its own position based on a signal received from a GPS (global positioning system), for example, a DGNSS (differential global navigation satellite system). Accordingly, if the GPS signal is jammed, a position information error occurs, which causes confusion for providing command control. The GPS signal has a weak signal strength so that the GPS signal is vulnerable to window jamming and can be easily jammed.
However, in the currently used vessel traffic control system, such a GPS jamming is not considered. That is, if the GPS jamming occurs, the ship transmits AIS information including erroneous position information and the erroneous AIS information is fused with the radar information so that an error occurs in the position which is displayed on the control system.
Even when the vessel traffic control system recognizes the GPS jamming, it is difficult to identify whether the AIS information or the fused information has an error so that incorrect control may be provided.